National Water-Quality Assessment Program

Estimation of Anthropogenic Nitrogen
and Phosphorus Inputs to the Land
Surface of the Conterminous United States—1992, 1997, and 2002

By Lori A. Sprague and Jo Ann M. Gronberg

Abstract

Anthropogenic inputs of nitrogen and phosphorus to each county in the conterminous United States and to the watersheds of 495 surface-water sites studied as part of the U.S. Geological Survey National Water-Quality Assessment Program were quantified for the years 1992, 1997, and 2002. Estimates of inputs of nitrogen and phosphorus from biological fixation by crops (for nitrogen only), human consumption, crop production for human consumption, animal production for human consumption, animal consumption, and crop production for animal consumption for each county are provided in a tabular dataset. These county-level estimates were allocated to the watersheds of the surface-water sites to estimate watershed-level inputs from the same sources; these estimates also are provided in a tabular dataset, together with calculated estimates of net import of food and net import of feed and previously published estimates of inputs from atmospheric deposition, fertilizer, and recoverable manure. The previously published inputs are provided for each watershed so that final estimates of total anthropogenic nutrient inputs could be calculated. Estimates of total anthropogenic inputs are presented together with previously published estimates of riverine loads of total nitrogen and total phosphorus for reference.

The county-level nutrient-input data described in this report are in the dataset Nutrient_input_county.xlsx that is available online at http://pubs.usgs.gov/sir/2012/5241/excel/Nutrient_input_county.xlsx. This dataset contains estimates of nitrogen (as N) and phosphorus (as P) inputs, expressed in kilograms, for each county in the conterminous United States.

The nutrient-input data for the watersheds of each of the 495 surface-water sites studied as part of the USGS NAWQA Program are in the dataset Nutrient_input_watershed.xlsx that is available online at http://pubs.usgs.gov/sir/2012/5241/excel/Nurient_input_watershed.xlsx. This dataset contains estimates of nitrogen (as N) and phosphorus (as P) inputs, expressed in kilograms.